1. Field of the Invention
The present invention relates to a solid state image sensing device and a photographing apparatus, and particularly, to a solid state image sensing device that can be applied to an auto focus camera for automatically performing focal point adjustment, and a photographing apparatus including the device.
2. Description of the Related Art
Recently, digital cameras including imaging devices such as a charge-coupled device (CCD) have become the photographing apparatuses of choice for many people. When photographing with CCD-equipped digital cameras, an object image is formed on the photo reception surface of the CCD, and the image is converted into an amount of signal charge in accordance with the quantity of light entering in the respective photo reception elements of the CCD. Then, the signal charge stored in the CCD is read out with respect for each pixel and converted into image data, and this image data is recorded in a recording medium such as a memory card.
In such digital cameras, just as in silver salt cameras, there have been proposals to include an auto focus function (hereinafter, referred to as AF) for automatically performing focal point adjustment of the object to be photographed. The AF function has a focusing lens for focal point adjustment and forms the object image on the CCD or the like, and focal point adjustment is performed by moving the focusing lens.
Most AF systems found in digital cameras are usually the so-called contrast AF system, which controls the focusing lens to move to the position where the contrast of the picture signal from the imaging device is the greatest.
Further, a system referred to as Through The Lens (TTL) phase contrast AF is used for single lens reflex cameras and the like. The TTL phase contrast AF system is a system for determining the focusing position by splitting a light beam and calculating the defocus amount (out-of-focus amount) from the phase contrast of the beam and controlling the movement of the focusing lens. In this system, since the defocus amount is known, focusing can be performed at high speed by making the out-of-focus amount zero.
Further, other AF methods have been proposed, such as a method for focusing by using multiple imaging devices like the technology disclosed in Japanese Patent Application Laid-Open (JP-A) No. 11-352393 (p. 1, FIG. 2), and a method for providing one of the multiple image sensing devices so as to be inclined relative to the optical axis, like the technology disclosed in JP-A No. 2001-281534 (p. 1, FIG. 1).
Nonetheless, in general contrast AF systems, since it is necessary to move the focusing lens over the entire moving range to detect contrast and find the position of the focusing lens where the contrast becomes the greatest, there is a problem in that it takes a longer time to focus. Further, in the TTL phase contrast AF system, there are problems in that the object image must be split for imaging and for focusing, and an optical system for exclusive use is required in order to obtain the phase contrast of light split for focusing.
There are also problems in the AF systems disclosed in JP-A Nos. 11-352393 and 2001-281534. Multiple imaging devices are required in both systems, and, in the AF system disclosed in JP-A No. 11-352393, an optical system such as a prism for splitting light is required, making the structure complex.